Conventionally, an ultrasonic sensor includes an ultrasonic transducer that has a piezoelectric device disposed on an inside of a bottom of a housing in a cylindrical shape, and a case having an opening for an assembly of the ultrasonic transducer inserted therethrough. The piezoelectric device is electrically coupled with a circuit board in the case with a lead wire. The lead wire is covered with sealing except for portions for electrical coupling. Japanese Patent Application No. 2004-159351 discloses an ultrasonic sensor having above-described structure.
In recent years, demand for use of a connector pin in place of the lead wire is gradually increasing because of an expected improvement in ease of assembly. For example, the ultrasonic transducer disclosed in Japanese Patent Application JP-A-H8-130795 or JP-A-H11-187491 has the connection pin (terminal pin, or lead terminal) on a base (terminal board) fixed on the housing, the connection pin extending toward outside of the housing in a piercing manner. The piezoelectric device in the ultrasonic transducer is electrically coupled with the circuit board by the connection pin.
However, the ultrasonic transducer disclosed in Japanese Patent Application JP-A-H8-130795 or JP-A-H11-187491 has the connection pin, one end portion (i.e., a root portion) of which is fixedly disposed on the base in a flat board shape in the housing, and a portion of the connection pin (i.e., a tip portion) extending outside of the housing is long relative to the portion of the connecting pin inside the housing. In addition, the connection pin is made of, for example, a material mainly containing copper in a thickness of 0.5 millimeter in diameter. Therefore, the connection pin may be bent (deformed) before being disposed on the case, that is, the terminals of the device may be bendingly displaced from a standard position. In this manner, the assembly of the device may be increasingly difficult because of the deformation/dislocation of the connection pin (the terminal pin). In other words, the ease of assembly of the ultrasonic sensor may be deteriorated.
Further, water intruded from a gap between the case and the transducer into the case may immerse an inner part of the ultrasonic sensor depending on a state of the assembly. In this case, the connection pin in the sensor may be corroded or may be short-circuited because of the intruded water.